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what to do when solution doesn't converge?

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Old   January 27, 2004, 09:30
Default what to do when solution doesn't converge?
  #1
Jenny
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Hi everyone,

I'm using SST model. My problem is a steady state fully developed turbulent curved duct flow. Outlet is set as opening with zero pressure and inlet with the velocity profile. The solution seems to stop converging after a certain no. of iteration. Can the separation in flow cause the SST model to fail?

http://www.angelfire.com/ab7/cfdwork/RMS.jpg http://www.angelfire.com/ab7/cfdwork/RMS2.jpg http://www.angelfire.com/ab7/cfdwork/RMS3.jpg
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Old   January 27, 2004, 11:31
Default Re: what to do when solution doesn't converge?
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Johnson
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Hi Jenny

I doubt this is the case. I would suggest looking at your residuals in Post first to see where the maximum values are. I would then examine the resolution of your mesh - very often you may only be able to achieve a certain level of convergence with a certain level of grid refinement.

Johnson

p.s. do you have re-circulation at your outlet ?
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Old   January 27, 2004, 13:22
Default Re: what to do when solution doesn't converge?
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Jan Rusås
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Nice residual curves! Try to define convergence! When I look at your residual curves I would be satisfied, I cant see your problem. Look in your outfile and check the global balances and see if they also are OK. (22 days left as a CFX user
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Old   January 27, 2004, 14:02
Default Re: what to do when solution doesn't converge?
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Robin
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Hi Jenny,

This doesn't look too bad. You may just be moving through a slow transient, increasing your timestep may help accelerate things.

Regards, Robin
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Old   January 27, 2004, 17:52
Default Re: what to do when solution doesn't converge?
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Glenn Horrocks
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Hi Jan,

22 days left? Are you moving across to the Dark Side?

Glenn
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Old   January 28, 2004, 05:00
Default Re: what to do when solution doesn't converge?
  #6
Jan Rusås
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Hi Glenn,

I have decided to sacrifice my self for a period and investigate what is going on at the Dark Side (21 days left)
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